Method and device for stretching and forming a foil blank and product produced herewith

ABSTRACT

The invention relates to a method and a device for stretching and forming a foil blank as well as to a product, which is produced by means of this method.

The invention relates to a method and a device for stretching andforming a foil blank as well as to a product produced herewith.

According to the state of the art, foil blanks are stretched biaxiallyprior to the deforming, for vacuum forming of bathtubs or innercontainers of refrigerators, e.g.. Through this, the foil thickness canalready be designed to be thinner or thicker in certain areas prior tothe deformation.

In the case of the production of inner parts for vehicles, such asinstrument panels or door side panels, the stretching degree of thesurface structure can additionally be influenced.

Such devices and methods are known from EP 1 140 470 B1, U.S. Pat. No.3,635,640, U.S. Pat. No. 3,579,718, JP 60049921 and JP 63197626, forexample.

All of these inventions have in common to pre-stretch the foil blankprior to the deformation. The fact that a defined sliding along of thefoil is not made possible during the forming process is a disadvantageof these described methods and devices.

Such a sliding along is realized in U.S. Pat No. 5,271,352 by means of asecond clamping frame 59, which is controlled via spring elements 54.Contrary to this state of the art, it is the object of the instantinvention to improve the known devices and methods.

According to a first aspect of the invention, this object is solved bymeans of a method for stretching and forming a foil blank, whereby afoil blank is elongated in one direction and the foil slides along inone direction during the deformation. A stretching of the foil blank inmore than one direction is also possible. Likewise, the foil can slidealong in more than one direction. In particular, the stretching can becarried out by means of a method or a device, respectively, as it isdescribed in DE 69909835 T2. Stretching is to be understood thereby asthe elongating or expanding, respectively, of the foil blank.Preferably, this takes place such that the form of the foil blank is notdistorted. In the case of a particularly suitable embodiment, thestretching takes place consistently in a plurality of directions.Sliding along is to be understood such that the foil can follow thetension, which is created by means of the forming process. A furtherelongation of the foil caused by the forming process can be avoidedcompletely or partly through this.

The sliding along can be controlled in the case of a particularlysuitable embodiment. In certain applications, however, it is alreadysufficient when the sliding along of the foil is not controlled, but iscreated independently via the tension of the foil in response to thedeformation.

Advantageously, the tension force can also be regulated. The tensionforce is to be understood as the force, by means of which the foil blankis stretched. This force can be adapted to the used foil blank or to thedesired process parameters, respectively, by means of a regulation.

The tension speed can also be regulated. The tension speed is to beunderstood as the speed, by means of which the foil blank is elongated.Here, a regulation also provides for an adaptation to the used foilblank as well as for a regulation of the process parameters and thus foran impact on the end product.

It is further advantageous when a forming aid is used during thedeformation and/or in a downstream step. While the deformation iscarried out from the inside by means of a forming tool, onto which thefoil is drawn, forming aids can act from the outside, so as to supportthe forming process. The foil can thus be pressed against the formingtool in areas, in which the foil does not come to rest on the formingtool when the foil is drawn onto the forming tool.

A second aspect of the invention comprises a device for stretching andforming a foil blank, in particular for carrying out a method accordingto the invention comprising a clamping frame and a holding element,wherein the holding element is slidingly supported in the foil plane, sothat it slides along in response to the forming.

In a preferred embodiment, the clamping frame is embodied with at leastone longitudinal and at least one cross beam. In particular, theclamping frame can be embodied as described in DE 69909835 T2. The foilplane is to be understood as the plane, in which the foil is held bymeans of the clamping frame. On the one hand, the heat expansion of thefoil is compensated by means of such a device. On the other hand, thefoil can be stretched in at least one axis and the foil can slide alongduring the forming process.

It is advantageous when the clamping frame can be displaced in x and/ory and/or z direction. The clamping frame can thus be moved completelyfreely in all spatial directions, for example relative to the formingtool.

It is further advantageous when the clamping frame is arranged so as tobe pivotable out of the foil transport plane about a center of gravity.The foil transport plane is to be understood as the plane, in which thefoil is transported into the clamping frame. The angle between formingtool and clamping frame can be changed through this. This provides foran improved contour-dependent sliding along of the foil at the surface,which is to be formed. This is advantageous in particular in the case ofcomplex formed parts.

Advantageously, the clamping frame is supported so as to be rotatableabout a fixed point. A clockwise rotation as well as a counter-clockwiserotation about any angles is thereby possible. The foil blank canthereby be optimally oriented towards the contour, which is to beformed. This rotation can take place in a controlled manner during theforming process.

According to a further embodiment of the invention, the clamping frameencompasses a clamping device, which can be moved in x and/or y and/or zdirection. It can be arranged, in particular, on the clamping frame.

The clamping device can preferably be supported so as to be rotatableabout a fixed point. It can be brought into contact with the foil blankby means of displacement as well as by means of rotation.

Finally, it is further advantageous when the device encompasses aforming aid. A forming aid is to be understood thereby as every device,which aids in better placing the foil blank onto the contours of theforming tool.

A last aspect of the invention comprises a product, which is produced bymeans of a method according to the invention and/or a device accordingto the invention.

The invention will be defined below in more detail by means of exemplaryembodiments with reference to the drawings.

FIG. 1 shows a device according to the invention prior to the forming,

FIG. 2 shows a device according to the invention during or after theforming, respectively,

FIG. 3 shows a device according to the invention comprising anadjustable clamping frame,

FIG. 4 shows a device according to the invention comprising a clampingframe having clamping elements,

FIG. 5 shows a device according to the invention comprising a clampingframe, which can be adjusted in foil plane,

FIG. 6 shows a device according to the invention comprising anadditional forming aid,

FIG. 7 shows a clamping frame and

FIG. 8 shows a clamping frame comprising attached clamping elements.

FIG. 1 shows a device 1 according to the invention for stretching andforming a foil blank 2 before the second step of the method according tothe invention, that is, the forming, is carried out. The foil 2 isclamped in the clamping frame 3. Said clamping frame consists of anupper clamping frame 4 and a lower clamping frame 5. The forming tool 6is not yet in contact with the foil 2.

As is illustrated in FIG. 2, in a next step, the forming tool 6 is movedinto the foil 2, which is held by the clamping frame 3. Through this,the foil adapts to the contours of the forming tool. According to theinvention, it is hereby possible for the foil to slide along in at leastone direction. When a sliding along is not possible, the foil is furtherexpanded by the forming. This effect is reduced or completely avoided bymeans of a partial or complete sliding along of the foil.

As is illustrated in FIG. 3, the clamping frame 3 can be adjusted in x,y and z direction. On the one side, the clamping frame was moved closerto the forming tool, while the distance on the other side of the formingtool has increased through this.

In addition, the clamping frame 3 can encompass clamping elements 7, 8,as is illustrated in FIG. 4. These are fastened on the upper clampingframe 4 and additionally hold the foil 2.

Finally, as is illustrated in FIG. 5, the clamping frame can bedisplaced in the foil plane. The clamping frame 3 is locatedconsiderably lower on the one side of the forming tool than on the otherside.

To provide for a better adaptation of the foil blank 2 to the contour ofthe forming tool 6, a forming aid 9 can additionally be used, as isillustrated in FIG. 8.

FIG. 7 shows a clamping frame 11 in top view. It consists of twoL-shaped frame parts 12, 13, which are in each case assembled on alongitudinal and a cross beam. They can be displaced with respect to oneanother, whereby the surface between the clamping frame parts 12, 14increases. In addition, the clamping frame is rotatable.

A clamping frame 21 is illustrated in FIG. 8 in top view. The clampingframe parts 22 and 23 are extended completely, whereby the foil isstretched to a maximum. Clamping elements 24, 25, 26, 27 and 28 areattached onto this clamping frame. They are arranged so as to beadjustable as well as rotatable and can thus be brought into contactwith a foil, which is clamped into the clamping frame, during theforming.

1. A method for stretching and forming a foil blank, wherein a foilblank is elongated in at least one direction and slides along in atleast one direction during the deformation.
 2. The method according toclaim 1, wherein the sliding along is controlled.
 3. The methodaccording to claim 1, wherein the clamping force is regulated.
 4. Themethod according to claim 1, wherein the clamping speed is regulated. 5.The method according to claim 1, wherein a forming aid is used duringthe deformation and/or in a downstream step.
 6. A device for stretchingand forming a foil blank, for carrying out a method according to claim1, comprising a clamping frame and a holding element, wherein theholding element is slidingly supported in the foil plane, so that itslides along in response to the forming.
 7. The device according toclaim 6, wherein the clamping frame can be displaced in x and/or yand/or z direction.
 8. The device according to claim 6, wherein theclamping frame is arranged so as to be pivotable out of the foiltransport plane about a center of gravity.
 9. The device according toclaim 6, wherein the clamping frame is supported so as to be rotatableabout a fixed point.
 10. The device according to claim 6, wherein theclamping frame encompasses a clamping device.
 11. The device accordingto claim 6, wherein the clamping device can be moved in x and/or yand/or z direction.
 12. The device according to claim 6, wherein theclamping device is supported so as to be rotatable about a fixed point.13. The device according to claim 6, wherein the device encompasses aforming aid.
 14. A product, which is produced by means of a methodaccording to claim 1 and/or by means of a device for stretching andforming a foil blank.